1. Field of the Invention
The present invention relates to an ink-jet recording system, and an ink-jet recording method, employing a recording medium that has superior colorforming performance and ink absorption and also can be prepared at a low cost. It also relates to an ink-jet recording system, and an ink-jet recording method, that can give a recorded image with superior sharpness, optical density and quality level.
2. Related Background Art
Hitherto known recording mediums used for inkjet recording include;
(1) those comprising an ordinary paper mainly composed of pulp, so made as to have a low degree of sizing as in filter paper or blotting paper (for example, those disclosed in Japanese Patent Laid-Open No. 52-53012): and (2) those comprising a substrate and a coat provided thereon using a pigment such as silica or zeolite which is porous, has a large oil absorption, and is capable of absorbing coloring components contained in ink.
The above recording mediums (1) are available in a low cost and also have excellent ink absorption, but may soak up ink so deeply into the fibrous layer of paper that the color-forming performance of the coloring material becomes poor. A phenomenon called feathering may also occur because of the absorption of ink along the fiber at the surface of the paper, to cause the phenomenon that a dot cannot be round but becomes jagged or a dot becomes so excessively large as to lower the resolution. As a result, no image with good quality can be obtained, disadvantageously.
For this reason, paper of a non-coated type has been chiefly used for the purpose of monochromatic recording or in terminals of personal computers in which the resolution may be relatively low and images with high density may not necessarily be required.
In the above recording mediums (2), coated papers comprising a substrate paper made of paper having a relatively higher degree of sizing (e.g., commercially available wood free paper) have been hitherto used as reported, for example, in Japanese Patent Laid-Open Nos. 58-132586 and 59 35977. Such coated papers comprise an ink-absorbing layer which is porous and uniform, so that there can be achieved appropriate ink absorption and images obtained images with excellent dot forms, color-forming performance and resolution.
However, in a recording system that requires an image with a higher quality level and higher resolution, a larger quantity of ink must be absorbed and fixed at a high speed. In this instance, a measure has been hitherto taken such that the coating weight of the ink-absorbing layer is increased and the void volume at the coat serving as the ink-absorbing layer is made larger. With an increase in the thickness of the coat, however, the problem of so-called dusting (peeling off of pigments on a surface) may arise, in which the coat is peeled from the substrate paper when the recording medium comes into contact with a carrying system in a recording apparatus. The dust thus formed not only contaminates the inside of the apparatus but also may cause clogging of nozzles of ink-jet heads, and hence is particularly questioned.
Moreover, in the course of manufacture, a large quantity of coating solution must be so rapidly dried that the binder contained in the coating solution may undergo migration, greatly causing a lowering of the strength of the coat or a lowering of the ink absorption. Such problems may be solved to a certain extent by making drying conditions milder or, for example, carrying out the coating dividedly several times. This, however, may also cause the problem that a high production cost results.
Means for solving these problems may include a method in which a paper with a low degree of sizing is used as the substrate paper and a porous pigment layer is provided thereon. For example, U.S. Pat. No. 4,478,910 discloses a recording medium comprising a substrate paper having a degree of sizing, of not more than 4 seconds and provided thereon a coat containing a silica having specific physical properties.
The recording medium of this type has the advantage that a recording medium having a good ink absorption can be obtained even when a relatively thin ink-receiving layer is provided, or the advantage that the coat to be provided may be in a small coating weight and hence the burden of the manufacture can also be small, resulting in a low cost and less generation of the dust. Even such a recording medium, however, has the following problems: (i) Because of penetration of a large quantity of ink deep into the substrate paper, a low print density may result. (ii) Because of the thin ink-receiving layer, which can little retain the ink, the form of dots is worsened when the ink is absorbed in the substrate paper, as pointed out in the recording mediums (1) previously discussed, or the ink droplets thus adhered may excessively run on the paper, resulting in a lowering of the resolution and print quality level.
On the other hand, in highly detailed full color recording that can obtain an image with a photographic tone, ink is required to be applied in a large quantity so that a high image density can be achieved. Moreover, in order to express multiple color tones, printing must be carried out using color inks for yellow (Y), magenta (M) and cyan (C), at least two or three of which are overlapped.
In this instance, the recording medium as mentioned above, which is different from the recording medium of the type to absorb ink with only the ink-receiving layer (i.e., the ink does not penetrate into the substrate paper) as in the case of the recording mediums (2) previously mentioned, is a recording medium in which the substrate paper absorbs and retains a greater part of the ink (in particular, solvent). Hence, there is a problem that the substrate may be swollen with the ink solvent and shrunk when dried, to cause cockling, or that the ink may penetrate through the back side of the substrate paper to cause strike-through.
The problem of cockling or strike-through is a problem that can be solved if the paper thickness is made larger. An excessively large thickness, however, may bring about the problem that the hand of the paper greatly differs from that of so-called plain paper, or the problem that the paper becomes so highly stiff that difficulties may arise in carrying. Hence, such a recording medium is not preferred as a recording medium having general-purpose properties.
Thus, although the problems of the strike-through and cockling occurring when high-density recording is performed are problems peculiar to the paper of this type, no means for completely solving these problems has been hitherto known.
In addition, these problems are closely concerned with not only the recording medium but also with inks, recording methods and processes, etc., and therefore they should be solved from the viewpoint of each of the inks, recording mediums, and printing methods. No means, however, has been known which can solve them through such recording systems or processes.